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Abstract Background Efficient and safe transection of biological tissue in liver surgery is strongly dependent on the ability to address both parenchymal division and hemostasis simultaneously. In addition to the conventional clamp crushing or finger fracture methods other techniques based on radiofrequency (RF) currents have been extensively employed to reduce intraoperative blood loss. In this paper we present our broad research plan for a new RF-assisted device for bloodless, rapid resection of the liver. Methods Our research plan includes computer modeling and in vivo studies. Computer modeling was based on the Finite Element Method (FEM) and allowed us to estimate the distribution of electrical power deposited in the tissue, along with assessing the effect of the characteristics of the device on the temperature profiles. Studies based on in vivo pig liver models provided a comparison of the performance of the new device with other techniques (saline-linked technology) currently employed in clinical practice. Finally, the plan includes a pilot clinical trial, in which both the new device and the accessory equipment are seen to comply with all safety requirements. Results The FEM results showed a high electrical gradient around the tip of the blade, responsible for the maximal increase of temperature at that point, where temperature reached 100°C in only 3.85 s. Other hot points with lower temperatures were located at the proximal edge of the device. Additional simulations with an electrically insulated blade produced more uniform and larger lesions (assessed as the 55°C isotherm) than the electrically conducting blade. The in vivo study, in turn, showed greater transection speed (3 ± 0 and 3 ± 1 cm2/min for the new device in the open and laparoscopic approaches respectively) and also lower blood loss (70 ± 74 and 26 ± 34 mL) during transection of the liver, as compared to saline-linked technology (2 ± 1 cm2/min with P = 0.002, and 527 ± 273 mL with P = 0.001). Conclusion A new RF-assisted device for bloodless, rapid liver resection was designed, built and tested. The results demonstrate the potential advantages of this device over others currently employed.

Abstract Background Radiofrequency ablation (RFA) of tumors by means of internally cooled electrodes (ICE) combined with interstitial infusion of saline may improve clinical results. To date, infusion has been conducted through outlets placed on the surface of the cooled electrode. However, the effect of infusion at a distance from the electrode surface is unknown. Our aim was to assess the effect of perfusion distance (PD) on the coagulation geometry and deposited power during RFA using ICE. Methods Experiments were performed on excised bovine livers. Perfusion distance (PD) was defined as the shortest distance between the infusion outlet and the surface of the ICE. We considered three values of PD: 0, 2 and 4 mm. Two sets of experiments were considered: 1) 15 ablations of 10 minutes (n ≥ 4 for each PD), in order to evaluate the effect of PD on volume and diameters of coagulation; and 2) 20 additional ablations of 20 minutes. The effect of PD on deposited power and relative frequency of uncontrolled impedance rises (roll-off) was evaluated using the results from the two sets of experiments (n ≥ 7 for each PD). Comparisons between PD were performed by analysis of variance or Kruskal-Wallis test. Additionally, non-linear regression models were performed to elucidate the best PD in terms of coagulation volume and diameter, and the occurrence of uncontrolled impedance rises. Results The best-fit least square functions were always obtained with quadratic curves where volume and diameters of coagulation were maximum for a PD of 2 mm. A thirty per cent increase in volume coagulation was observed for this PD value compared to other values (P < 0.05). Likewise, the short coagulation diameter was nearly twenty five per cent larger for a 2 mm PD than for 0 mm. Regarding deposited power, the best-fit least square function was obtained by a quadratic curve with a 2 mm PD peak. This matched well with the higher relative frequency of uncontrolled impedance rises for PD of 0 and 4 mm. Conclusion Saline perfusion at around 2 mm from the electrode surface while using an ICE in RFA improves deposition of energy and enlarges coagulation volume.

Resonant power conversion is a key enabling technology of dc-dc conversion, inverters and contactless energy transfer systems. This paper presents an analytical model of the series resonant half-bridge topology aimed at improving the design, control, and efficiency of resonant power converters. The main contribution is a closed-form expression of the main converter waveforms as well as output power and efficiency. This model enables a fast design-space exploration, as well as the implementation of advanced control techniques using adaptive control or real-time emulation, significantly improving the converter operation. The analytical expressions presented have been applied and verified through a half-bridge series resonant inverter applied to induction heating applications, proving the accuracy and effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Resonant converters featuring soft switching are commonly used in domestic induction heating applications due to their high efficiency and high power density. In this paper, the design and implementation procedure of an improved efficiency and low-profile resonant inverter for induction heating applications is presented. The proposed converter is based on a multi-MOSFET cell implementation, reducing the equivalent on-state resistance per chip-area. By using automotive-grade MOSFET devices, a converter capable of delivering up to 4 kW has been built, reducing conduction losses against the classical IGBT-based converter. In addition to this, the reduced switching times of MOSFET devices decrease switching losses, further increasing the conversion efficiency. The main design challenges including the device selection, gate drive circuit, and cooling have been addressed. As a conclusion, a low-profile implementation without fan and heat sink is obtained, which significantly improves state-of-the-art technology in terms of efficiency and power density. [ABSTRACT FROM AUTHOR]

Induction heating (IH) technology is nowadays widely present in domestic appliances because of its cleanness, high efficiency, and faster heating process. All of these advantages are due to its heating process, where the pot is directly heated by the induced currents generated with a varying magnetic field. As a result, the glass where the pot is supported is not directly heated and, consequently, efficiency and heating times are improved. IH systems are based on dc-link inverters to generate the required alternating current to feed the inductor. Usually, resonant converters are used to achieve higher efficiencies and power densities. In such systems, the maximum output power and efficiency are achieved at the resonant frequency, and the switching frequency is increased to reduce the output power. As a consequence, in these converters, the efficiency is also reduced in the low-medium output power range. This paper proposes the use of the half-bridge inverter in two operating modes to achieve higher efficiency in a wide output power range. The power converter topology can be reconfigured by changing the resonant capacitors through electromechanical relays. As a consequence, the entire efficiency of the cooking process is improved with a cost-effective procedure. [ABSTRACT FROM AUTHOR]

This paper proposes a model of the mutual impedance between ring-type coils used in domestic induction hobs. Recent developments in these appliances have focused on flexible cooking surfaces, including adjustable-size or total-active surfaces. Flexible cooking surfaces are implemented by means of several small ring-type closely arranged coils, each one supplied by a resonant inverter. The basic winding is a ring-type circular small coil, whose self-impedance has been reported previously. In this paper, the coupling between coils in terms of impedance is derived. The coils are modeled as axisymmetric current density distributions with parallel revolution axes. The mutual impedance between the coils is obtained considering two media representing the load and the ferrite, respectively. Experimental measurements have been performed to validate the results. [ABSTRACT FROM AUTHOR]

Domestic induction cookers operation is based on a resonant inverter which supplies medium-frequency currents (20-100 kHz) to an inductor, which heats up the pan. The variable load that is inherent to this application requires the use of a reliable and load-adaptive control algorithm. In addition, a wide output power range is required to get a satisfactory user performance. In this paper, a control algorithm to cover the variety of loads and the output power range is proposed. The main design criteria are efficiency, power balance, acoustic noise, flicker emissions, and user performance. As a result of the analysis, frequency limit and power level limit algorithms are proposed based on square wave and pulse density modulations. These have been implemented in a field-programmable gate array, including output power feedback and mains-voltage zero-cross-detection circuitry. An experimental verification has been performed using a commercial induction heating inverter. This provides a convenient experimental test bench to analyze the viability of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In many applications, efficiency and service quality are improved with an appropriate power control. This paper focuses on a power-measurement method designed to deal with medium/high frequencies (tens to hundreds of kilohertz). It requires a previous knowledge of application and exploits some characteristics of the power topology and control, in this case, a full-bridge series resonant inverter. It is a new method based on a low-cost analog circuit that integrates the high-frequency load current, in order to reduce the computational complexity of measuring power. Harmonic analysis is carried out to determine the AID converter requirements, and the theoretical results are verified using a digital-signal-processor (DSP)-based experimental setup. The power measurement may be implemented on the microcontroller or low-performance DSP used to control the power stage, with an error below of 2% independent of the load and mains variations. [ABSTRACT FROM AUTHOR]

Multiple-burner induction-heating cooking appliances are suitable for using multiple-output inverters. Some common approaches use several single-output inverters or a single-output inverter multiplexing the loads along the time periodically. By specifying a two-output series-resonant high-frequency inverter, a new inverter is obtained fulfilling the requirements. The synthesized converter can be considered as a two-output extension of a full-bridge topology. It allows the control of the two outputs, simultaneously and independently, up to their rated powers saving component count compared with the two-converter solution and providing a higher utilization of electronics. To verify theoretical predictions, the proposed converter is designed and tested experimentally in an induction-heating appliance prototype. A fixed-frequency control strategy is digitally implemented with good final performances for the application, including ZVS operation for active devices and a quick healing function. Although the work is focused on low-power induction heating, it can be probably useful for other power electronic applications. [ABSTRACT FROM AUTHOR]

We present a simple method to calculate the winding resistance of a litz-wire inductor in an induction cooking appliance, taking into account eddy-current losses, including conduction losses and proximity-effect losses. The method, which uses numerical calculation of the magnetic field, can be used to determine the optimum number of strands in the litz wire. The effects of the temperature on the winding total resistance are included in the calculation. We have built a prototype to verify the calculation method and its limitations. We consider the accuracy limits of the method. [ABSTRACT FROM AUTHOR]

This paper presents and analyzes the asymmetrical voltage-cancellation (AVC) control, a generalized control technique for resonant Inverters. It is applied to the popular full-bridge series resonant inverter. The proposed control technique achieves helter efficiency performances than conventional fixed-frequency control strategies, while considering zero-voltage-switching operation, output power and load variations. The theoretical results are verified experimentally, using a prototype for an induction-healing cooking appliance. [ABSTRACT FROM AUTHOR]

Electroporation is a phenomenon that consists of increasing the permeability of the cell membrane by means of high-intensity electric field application. Nowadays, its clinical application to cancer treatment is one of the most relevant branches within the many areas of electroporation. In this area, it is essential to apply homogeneous treatments to achieve complete removal of tumors and avoid relapse. It is necessary to apply an optimized transmembrane potential at each point of the tissue by means of a homogenous electric field application and appropriated electric field orientation. Nevertheless, biological tissues are composed of wide variety, heterogeneous and anisotropic structures and, consequently, predicting the applied electric field distribution is complex. Consequently, by applying the parallel-needle electrodes and single-output generators, homogeneous and predictable treatments are difficult to obtain, often requiring several repositioning/application processes that may leave untreated areas. This paper proposes the use of multi-electrode structure to apply a wide range of electric field vectors to enhance the homogeneity of the treatment. To achieve this aim, a new multi-electrode parallel-plate configuration is proposed to improve the treatment in combination with a multiple-output generator. One method for optimizing the electric field pattern application is studied, and simulation and experimental results are presented and discussed, proving the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

Summary background data. Radiofrequency ablation (RFA) is a relatively new technology for the local destruction of liver tumors. Development of recent devices has enabled the creation of larger lesions. Nevertheless, treating liver tumors larger than 2.5 cm in diameter often requires multiple overlapping ablations to encompass the tumor and the surrounding healthy tissue rim with an increasing risk of local recurrence.Material and methods. RFA (480 kHz) of the liver using our method was undertaken on a total number of 15 healthy farm pigs with (Group B, n = 8) or without (Group A, n = 5) the Pringle maneuver via laparotomy. The pigs were followed and euthanized on the seventh day of the experiment. Livers were removed for histological assessment. Time of the procedure, impedance, current, power output, energy output, temperatures in the liver, central temperature of the animal, volume size of the lesion, and delivered energy per lesion volume were determined and compared among groups. Additionally a regularity ratio (RR) was determined by gross examination of the specimen and scored (0–3) taking into account regularity and predictability of the ablation with pathologic assessment.Results. With both methods, ellipsoid lesions were created between the two probes. In both groups tissue impedance fell with time (r = −0.47, P < 0.01 and r = −0.34, P < 0.05, in Groups A and B, respectively). The mean lesion size achieved with the Pringle maneuver was the largest lesion size described in the literature for any RFA method in vivo and was greater in Group B than in Group A (123.22 cm3 ± 49.62 and 52.40 cm3 ± 23.59, respectively, P < 0.05). A better regularity and predictability evaluated by RR was observed in Group B compared to Group A (1.88 ± 1.35 and 0.40 ± 0.55, respectively, P < 0.05). Five major complications were described and attributed primarily to failure in isolation from hypertermic lesions.Conclusions. Our new bipolar saline-enhanced electrode with Pringle maneuver achieves large hepatic ablations in in vivo pig liver. These large lesions are well-tolerated by the animal when thermal injuries to adjacent structures are avoided. [Copyright &y& Elsevier]

One of the strategies for enlarging coagulation zone dimensions during RF ablation of liver tumours is to infuse saline solutions into the tissue during ablation. The aim of this study was to evaluate experimentally whether the creation of a small coagulation adjacent to a bipolar RF applicator and prior to perfused RF ablation would allow enlargement of the coagulation zone. Thirty bipolar RF ablations (group A, n = 15; group B, n = 15) were performed in excised bovine livers. Additionally, in group B a monopolar RF application (60 W, 20 s) was performed before bipolar ablation using three small additional electrodes. Electrical parameters and dimensions of the ablation zone were compared between groups. Despite the fact that all three ablation zone diameters were greater in group B, only one of the minor diameters was significantly longer (5.52 +/- 0.66 cm versus 4.87 +/- 0.47 cm). Likewise, volume was significantly bigger in group B (100.26 +/- 24.10 cm(3) versus 79.56 +/- 15.59 cm(3)). There were no differences in the impedance evolution, allowing a relatively high constant power in both groups (around 90 W). The efficacy of delivering energy (expressed as the delivered energy per coagulation volume) was significantly better in group B, showing a lower value (578 J cm(-3) versus 752 J cm(-3)). These results suggest that the creation of small ablation zones prior to saline infusion improves the performance of this perfusion system, and hence the total volume.